Pascal’s Law

Pascal’s law states that when pressure is applied at any part of an enclosed liquid, it is transmitted undiminished to every point of the liquid as well as to the walls of the container.

This law is also known as the law of transmission of liquid pressure.

Applications of Pascal’s Law

Hydraulic Press or Balance or Jack or Lift

It is a simple device based on Pascal’s law and is used to lift heavy loads by applying a small force. Let a force F1 be applied to the smaller piston of area A1. On the other side, the piston of large area A2 is attached to a platform where heavy load may be placed.

The pressure on the smaller piston is transmitted to the larger piston through the liquid filled in-between the two pistons. Since the pressure is same on both the sides,

Pressure on the smaller piston,

P = force / area

P = F1/A1

According to Pascal’s law, the same pressure is transmitted to the larger cylinder of area A2. Hence the force acting on the larger piston

F2 = pressure × area = F1/A1 × A2

Force F2 > F1 by an amount equal to the ratio (A2/A1)

With slight modifications, the same arrangement is used in hydraulic press, hydraulic balance, and hydraulic Jack, etc.

Hydraulic Jack or Car Lifts

At automobile service stations, buses and trucks are raised to the desired heights so that a mechanic can work under them. This is done by applying pressure, which is transmitted through a liquid to a large surface to produce sufficient force needed to lift the car.

Hydraulic Brakes

While traveling in a bus or a car, a driver applies a little force by his foot on the brake paddle to stop the vehicle. The pressure so applied gets transmitted through the brake oil to the piston of slave cylinders, which, in turn, pushes the break shoes against the break drum in all four wheels, simultaneously. The wheels stop rotating at the same time and the vehicle comes to stop instantaneously.